... actually i forgot that the default fopen mode is "rb" ... anyhow, here
is what's supposed to happen:
$ touch bug.txt; chmod 0777 bug.txt; php -r '$o=new
SplFileObject("bug.txt");var_dump($o->fwrite("test"));var_dump(error_get_last());'
PHP Notice:  SplFileObject::fwrite(): Write of 4 bytes failed with errno=9
Bad file descriptor in Command line code on line 1
bool(false)
array(4) {
  ["type"]=>
  int(8)
  ["message"]=>
  string(81) "SplFileObject::fwrite(): Write of 4 bytes failed with errno=9
Bad file descriptor"
  ["file"]=>
  string(17) "Command line code"
  ["line"]=>
  int(1)
}

changing the code to SplFileObject("bug.txt", "rb");
makes the code work, but there's still the issue with cygwin's php's
SplFileObject::fwrite() not noticing the write error

On Sat, 1 Oct 2022 at 18:47, Hans Henrik Bergan <divinity76@gmail.com>
wrote:

> running PHP 7.3.7 in Cygwin 3.3.6, and SplFileObject::fwrite seems
> completely broken.
> to reproduce:
> $ touch bug.txt; chmod 0777 bug.txt; php -r '$o=new
> SplFileObject("bug.txt");var_dump($o->fwrite("test"));var_dump(error_get_last());'
> int(0)
> NULL
>
> so both fwrite() and error_get_last() failed to pick up that there was an
> error,
> but strace reveals:
> 67 487251 [main] php 1693 __set_errno: ssize_t write(int, const void*,
> size_t):1350 setting errno 9
> 60 487311 [main] php 1693 write: -1 = write(3, 0x6FFFFFE65BF8, 4), errno 9
>
> errno 9 probably means: 9 EBADF Bad file descriptor.
>